This application is a continuation-in-part of U.S. patent application Ser. No. 203,746 entitled "Scan Converter System" and filed on Nov. 3, 1980, now abandoned.
In instruments such as ultrasound scanners that are used to produce images of a cross-section of the heart and other organs of a patient, the data signals represent analog information along radial lines of a sector. Reproduction of the images in the same format is objectionable because of the voids between the radial lines. As a consequence of this, the modern approach is to sample the data along radial rays and write the sampled data into a digital display memory, sometimes referred to as a digital scan converter. A description of this approach may be found in the article by J. Ophir and N. F. Maklad, entitled "Digital Scan Converters in Diagnostic Ultrasound Imaging", Proc. IEEE, Vol. 67, No. 4, April 1979. Samples of the analog data along each radial line are obtained at points having a uniform spacing of such dimension as to satisfy the Nyquist criteria. Their x,y coordinates are determined from their R,.theta. coordinates and the samples are transferred to the nearest display point in a display memory. By resorting to this point-to-point translation rather than true image reconstruction, a number of problems occur, but the one of greatest significance is the moir/e/ patterns that result from the fact that some display points in the display memory receive no information.
The moir/e/ pattern can be eliminated by fill-in techniques, such as translating to an empty display point data from the sample written into the display point on either side, but artifactual boundaries or discontinuities are introduced into the image that are highly objectionable.
Another attempt to deal with the moir/e/ problem has been to insert one or more radial lines of interpolated data between the actual radial lines of data prior to translating the information to the display points of a display memory as previously described. Whereas the moir/e/ is reduced, the fact that many display points receive more than one sample and the fact that the last sample received is the only one that is reproduced in the image cause discontinuities that often manifest themselves in artificial "contrastiness" and radial tearing of the image. Attempted solutions to this problem have included peak detection or averaging of the samples written into a given display point. Although this does some good, it does not solve the problem. Furthermore, the read-modify-write operations involved require complex circuitry that in the present state of the art may not function with sufficient speed to permit real-time operation at desired sector scanning rate of thirty a second.